Json String to Java Object Avro

json java avro

2022-09-02 19:59:50

我正在尝试将Json字符串转换为具有Avro Schema的通用Java对象。

下面是我的代码。

String json = "{\"foo\": 30.1, \"bar\": 60.2}";
String schemaLines = "{\"type\":\"record\",\"name\":\"FooBar\",\"namespace\":\"com.foo.bar\",\"fields\":[{\"name\":\"foo\",\"type\":[\"null\",\"double\"],\"default\":null},{\"name\":\"bar\",\"type\":[\"null\",\"double\"],\"default\":null}]}";

InputStream input = new ByteArrayInputStream(json.getBytes());
DataInputStream din = new DataInputStream(input);

Schema schema = Schema.parse(schemaLines);

Decoder decoder = DecoderFactory.get().jsonDecoder(schema, din);

DatumReader<Object> reader = new GenericDatumReader<Object>(schema);
Object datum = reader.read(null, decoder);

我得到“org.apache.avro.AvroTypeException：Expected start-union。有VALUE_NUMBER_FLOAT“例外。

如果我在架构中没有联合，则相同的代码有效。有人可以解释并给我一个解决方案。

答案 1

对于任何使用Avro - 1.8.2的人来说，现在不能直接在软件包外实例化。您可以按照以下代码所示使用它：JsonDecoderorg.apache.avro.ioDecoderFactory

String schemaStr = "<some json schema>";
String genericRecordStr = "<some json record>";
Schema.Parser schemaParser = new Schema.Parser();
Schema schema = schemaParser.parse(schemaStr);
DecoderFactory decoderFactory = new DecoderFactory();
Decoder decoder = decoderFactory.jsonDecoder(schema, genericRecordStr);
DatumReader<GenericData.Record> reader =
            new GenericDatumReader<>(schema);
GenericRecord genericRecord = reader.read(null, decoder);

答案 2

感谢礼萨。我找到了这个网页。它介绍了如何将 Json 字符串转换为 avro 对象。

http://rezarahim.blogspot.com/2013/06/import-org_26.html

他的代码的关键是：

static byte[] fromJsonToAvro(String json, String schemastr) throws Exception {
  InputStream input = new ByteArrayInputStream(json.getBytes());
  DataInputStream din = new DataInputStream(input);

  Schema schema = Schema.parse(schemastr);

  Decoder decoder = DecoderFactory.get().jsonDecoder(schema, din);

  DatumReader<Object> reader = new GenericDatumReader<Object>(schema);
  Object datum = reader.read(null, decoder);

  GenericDatumWriter<Object>  w = new GenericDatumWriter<Object>(schema);
  ByteArrayOutputStream outputStream = new ByteArrayOutputStream();

  Encoder e = EncoderFactory.get().binaryEncoder(outputStream, null);

  w.write(datum, e);
  e.flush();

  return outputStream.toByteArray();
}

String json = "{\"username\":\"miguno\",\"tweet\":\"Rock: Nerf paper, scissors is fine.\",\"timestamp\": 1366150681 }";

String schemastr ="{ \"type\" : \"record\", \"name\" : \"twitter_schema\", \"namespace\" : \"com.miguno.avro\", \"fields\" : [ { \"name\" : \"username\", \"type\" : \"string\", \"doc\"  : \"Name of the user account on Twitter.com\" }, { \"name\" : \"tweet\", \"type\" : \"string\", \"doc\"  : \"The content of the user's Twitter message\" }, { \"name\" : \"timestamp\", \"type\" : \"long\", \"doc\"  : \"Unix epoch time in seconds\" } ], \"doc:\" : \"A basic schema for storing Twitter messages\" }";

byte[] avroByteArray = fromJsonToAvro(json,schemastr);

Schema schema = Schema.parse(schemastr);
DatumReader<Genericrecord> reader1 = new GenericDatumReader<Genericrecord>(schema);

Decoder decoder1 = DecoderFactory.get().binaryDecoder(avroByteArray, null);
GenericRecord result = reader1.read(null, decoder1);